1. Field of the Invention
The present invention relates to a rotary sensor, and more particularly to a rotary sensor capable of accurately detecting an angle of rotation to be transmitted from the outside.
2. Description of the Related Art
With reference to the drawings, the description will be made of a conventional rotary sensor.
FIG. 18 is a sectional view showing a conventional rotary sensor under application by Japanese Patent Laid-Open Application No. 2000-74611 and U.S. Pat. Ser. No. 09/388,392 corresponding thereto, FIG. 19 is a sectional view showing a conventional rotor for rotary sensor, FIG. 20 is a front view showing the conventional rotor for rotary sensor, FIG. 21 is a perspective view showing a conventional elastic member for rotary sensor, FIG. 22 is a front view showing a conventional driving shaft for rotary sensor, and FIG. 23 is a side view showing a conventional driving shaft for rotary sensor.
As shown in FIG. 18, the conventional rotary sensor has a casing 30 disposed which is substantially cylindrical in external shape and is made of thermosetting resin or the like, and this casing 30 has a front side plate 30a formed on the upper side thereof, and at the central portion of the front side plate 30a, there is formed a shaft hole 30b. 
Inside the casing 30, there is formed a substantially cylindrical storage portion 31, and within the storage portion 31, there is housed a rotor 32. This rotor 32 has, as shown in FIGS. 19 and 20, a disk-shaped collar portion 32a, and at the underside of the collar portion 32a, a shaft portion 32b having a small outside diameter, and on the upper side, a bearing portion 32c having a large outside diameter are projectingly formed respectively.
The bearing portion 32c is formed with a difference in level 32d, a tip end portion 32e above the difference in level 32d is formed to have a smaller outside diameter than the difference in level 32d. Thus, the tip end portion 32e is inserted into the shaft hole 30b of the casing 30 in such a manner that the rotor 32 can rotate with the center line A as the center of rotation within the storage portion 31.
On the side of the collar portion 32a at the underside, there are projectingly formed a plurality of protrusions 32f, on the basis of which a moving contact piece to be described later will be positioned to be mounted.
At the center of rotation of the bearing portion 32c, there is formed an engaging hole 33 having a predetermined depth, and this engaging hole 33 consists of a flat portion 33a and a circular arc portion 33b, is shaped like a D-character as viewed from the front, and a periphery of the inlet portion 33c is chamfered for formation.
Adjacent the flat portion 33a of the engaging hole 33, and in parallel to the flat portion 33a, there is formed a groove portion 34 having predetermined depth and width dimensions.
Between the groove portion 34 and the flat portion 33a of the engaging hole 33, there is formed a partition wall 35, and this partition wall 35 is formed with an open portion 36 for communicating the engaging hole 33 to the groove portion 34 at a predetermined depth from the inlet portion 33c of the engaging hole 33. Since this open portion 36 is, as shown in FIG. 20, formed to be smaller than the width dimension of the groove portion 34, the partition wall 35 protrudes on both sides of the open portion 36.
The groove portion 34 is adapted to be inserted by an elastic member 37 including a plate spring. As shown in FIG. 21, a proximal portion 37a is stamped out by means of a press or the like to form a portion left by stamping out 37b, and the elastic member 37 is formed with a tongue piece-shaped elastically-contacted portion 37c and a loose-stop portion 37d enclosed by the portion left by stamping out 37b. 
The elastically-contacted portion 37c is projectingly formed upwardly by being curved in a mountain shape, and at the underside on the opposite side to a direction that this elastically-contacted portion 37c projects, there is provided the loose-stop portion 37d formed by raising up.
The elastic member 37 has a through-hole 37e having a predetermined hole diameter formed by stamping out at the curved apex portion of the elastically-contacted portion 37c, and at the end portion on the right side, there is formed a supporting portion 37f having a predetermined height dimension, bent downward in the same direction as the loose-stop portion 37d. 
Thus, when the elastic member 37 is inserted into the groove portion 34, the loose-stop portion 37d on one side comes into elastic contact with between the side walls of the lower part of the groove portion 34, while the supporting portion 37f on the other side abuts against the side wall of the groove portion 34.
By means of an elastic force of the loose-stop portion 37d, the flat proximal portion 37a mainly comes into elastic contact with the partition wall 35 at the side of the open portion 36 so that the elastic member 37 is prevented by the groove portion 34 from falling off and is held.
Also, when the elastic member 37 is inserted into the groove portion 34, the curved apex portion of the elastically-contacted portion 37c is adapted to go through the open portion 36 for projecting on the engaging hole 33 side to be positioned.
Also, on the side, on which the shaft portion 32b at the underside of the collar portion 32a of the rotor 32, has been formed, there is mounted a moving contact piece 38 with a spring operation, which is a part of the angle of rotation detecting member. This moving contact piece 38 is, as shown in FIG. 18, positioned by a plurality of protrusions 32f formed on the collar portion 32a, and is fixed to the rotor 32 by means of thermal caulking or the like.
On a side opposite to the surface, onto which the moving contact piece 38 has been mounted, a resistor substrate 39 is positioned with a predetermined clearance spaced within the casing 30, and is fixed by means of adhesive or the like.
On the surface of the resistor substrate 39, a resistor pattern (not shown) is formed by means of printing or the like, and the moving contact piece 38 is adapted to come into elastic contact with this resistor pattern.
Also, at the central portion of the resistor substrate 39, there is formed a shaft hole 39a, through which the shaft portion 32b of the rotor 32 is inserted. The angle detecting member is constituted by the moving contact piece 38 and the resistor substrate 39 having the resistor pattern.
On the right side of the resistor substrate 39 shown in FIG. 18, a plurality of substantially L character-shaped external terminals 40 are made integral with the casing 30 by means of insert molding or the like. Correspondingly to the resistor pattern (not shown), the external terminals 40 are connected to a terminal 50 drawn out of the end surface of the resistor substrate 39 by means of soldering or the like.
At the underside of the resistor substrate 39, a cover body 41 for closing the storage portion 31 within the casing 30 as a cover is mounted by means of adhesive or the like in such a manner that the interior of the storage portion 31 is hermetically sealed. On the side of the interior of the cover body 41 on the center line A, such a bearing portion 41a as shown in FIG. 18 is projectingly formed, and the shaft portion 32b of the rotor 32 is supported by this bearing portion 41a so that the rotor 32 is prevented from moving in a direction perpendicular to the direction of the center line A for causing no clutter.
In order to detect an angle of rotation of a throttle valve of, for example, an automobile or the like through the use of a conventional rotary sensor having the above-described structure, the casing 30 is first mounted to the main body of a throttle body (not shown). Then, as shown in FIG. 18, the driving shaft 42 coupled to the throttle valve is inserted into the engaging hole 33 of the rotor 32 for being positioned.
This driving shaft 42 has, as shown in FIGS. 22 and 23, a flat portion 42b formed at the circular rod-shaped tip end portion 42a, and the tip end portion 42a is D character-shaped. The driving shaft 42 is adapted to reciprocatively rotate within a predetermined range of angle of rotation by interlocking with the rotation of the throttle valve on the automobile side.
This driving shaft 42 is inserted into the engaging hole 33 of the rotor 32, and in this state, the elastically-contacted portion 37c of the elastic member 37 is brought into elastic contact with the flat portion 42b of the driving shaft 42.
Next, the driving shaft 42 is generally held so as to slightly operate (move) in a back-and-forth direction of the axial direction, and the description will be made of an operation in this case.
First, as regards the operation (movement) in the forward direction in which the driving shaft 42 goes out of the engaging hole 33 of the rotor 32, when the driving shaft 42 slightly moves in the forward direction, the elastically-contacted portion 37c of the elastic member 37 slightly moves in the forward direction with the movement of the driving shaft 42. With the movement of this elastic member 37, the rotor 32, by which the elastic member 37 is locked, slightly moves in the forward direction so that the clearance between the rotor 32 and the resistor substrate 39 is to expand.
The expansion of this clearance slightly deviates an elastically-contacted position of the moving contact piece 38 fixed to the rotor 32 with the resistor pattern of the resistor substrate 39 or reduces the contact pressure.
As described above, according to the conventional rotary sensor, when the driving shaft 42 moves in the forward direction that it goes out of the engaging hole 33 of the rotor 32, the rotor 32 moves in the forward direction together with the driving shaft 42, whereby the elastically-contacted position of the moving contact piece 38 with the resistor pattern of the resistor substrate 39 is slightly deviated, and this deviation slightly deviates a predetermined resistance value, leading to a problem that the output value becomes unstable.
The rotary sensor according to the present invention solves the above-described problem, and its object is to provide a rotary sensor capable of maintaining stable electrical performance.
According to the present invention, there is provided a rotary sensor, comprising: a rotor having a hole portion and a collar portion, into the hole portion of which a driving shaft is inserted; a casing for rotatably supporting the rotor, having a supporting portion opposite to a surface of the collar portion; an angle detecting member for being operated by rotation of the rotor; and a first elastic member for being held in the hole portion of the rotor and being brought into elastic contact with a peripheral surface of the driving shaft for transmitting rotation of the driving shaft to the rotor, wherein between the supporting portion and the collar portion, there is disposed a second elastic member for pressing the collar portion in the axial direction of the driving shaft, wherein a pressing force of the second elastic member is greater than a frictional force generated between the driving shaft and the first elastic member when the driving shaft moves in a back-and-forth direction of the axial direction, and wherein when the driving shaft moves in the forward direction to go out of the rotor, the structure is arranged such that a pressing force of the second elastic member prevents the rotor from moving forward.
Also, the rotary sensor according to the present invention has the first elastic member made of a flat plate-shaped metallic material, which is constituted by a bent portion bent into a U-character shape, and a plate spring having a spring portion and a holding portion, which are extendedly provided from the bent portion respectively and oppose to each other, the spring portion is brought into elastic contact with the peripheral surface of the driving shaft, and the holding portion abuts against the inner wall of the hole portion.
Also, the rotary sensor according to the present invention has the bent portion disposed on the bottom wall side of the hole portion of the rotor.
Also, the rotary sensor according to the present invention is provided, within the hole portion, with :a flat surface portion provided at a part of the inner wall of the hole portion, and parallel to the axial direction of the driving shaft; and a protruded portion opposite to a part of the flat surface portion, in a clearance provided between the flat surface portion and the protruded portion, a bent portion is located, and a spring portion located at any other place than the clearance is brought into elastic contact with the driving shaft.
Also, in the rotary sensor according to the present invention, the plate spring has a kerf extending from the bent portion toward the free end of the holding portion, the flat surface portion of the hole portion is formed with a ridge portion extending in the axial direction of the driving shaft, and the ridge portion is engaged with the kerf.
Also, in the rotary sensor according to the present invention, the holding portion of the plate spring is formed with a raised-up portion raised up in the direction of the free end of the holding portion, the flat surface portion of the hole portion is provided with a recess, the raised-up portion is engaged with the recess, and the plate spring is prevented from falling off forward in the axial direction of the driving shaft.
Also, in the rotary sensor according to the present invention, at the free end of the spring portion of the plate spring, there is formed a substantially circular arc-shaped elastically-contacted portion in a direction perpendicular to the axial direction of the driving shaft, and the elastically-contacted portion is brought into elastic contact with the peripheral surface of the driving shaft.